1. Field of the Invention
The invention concerns a flexible filter bag that is open at one end to receive a fluid to be filtered under pressure while the filter bag is fitted either into or over a rigid filter basket. The invention also concerns a method for making such a bag.
2. Description of the Related Art
Liquid filtering apparatus employing a flexible filter bag has been known since at least 1925. As indicated in Tafara U.S. Pat. No. 4,545,833, most filter bags have sewn seams extending both longitudinally and across the closed end. Leakage through holes formed by the sewing needle permits unfiltered liquid to pass, thus contaminating the filtered liquid. The open end of the bag is folded inwardly around a thin metal ring by which the bag is sealed to the filtering apparatus. The longitudinal seam can prevent the bag from fitting tightly against the ring, thus providing an additional leakage site.
Tafara's answers to the needle-holes leakage was to employ heat and pressure to form fused seams extending both longitudinally and across the closed end of the filter bag. Because such a fused longitudinal seam should be flush with the surface of the filter bag, it should also avoid the leakage at the metal ring that had been encountered with sewn seams. Among possibly significant drawbacks in Tafara's bag are the difficulty of determining whether the fused seams are completely sealed. Also, the fused seams reduce the flexibility of the bag.
A flexible liquid-filtering bag which has sewn longitudinal and end seams is shown in UK Patent Application No. GB 2,168,906A which was published July 2, 1985. See also Gravley U.S. Pat. No. 3,937,621 and Schmidt, Jr. U.S. Pat. No. 4,247,394.